ECG (electrocardiogram) is a test that measures the electrical activity of the heart. The heart is a muscular organ that beats in rhythm to pump the blood through the body. The signals that make the heart’s muscle fibres contract come from the sinoatrial node, which is the natural pacemaker of the heart.In an ECG test, the electrical impulses made while the heart is beating are recorded and usually shown on a piece of paper. This is known as an electrocardiogram, and records any problems with the heart’s rhythm, and the conduction of the heart beat through the heart which may be affected by underlying heart disease.